Conventional multiblade air blowers of this type have a structure in which the blade ends and orifice are axially overlaid. (Refer to Patent Document 1.)
The conventional multiblade air blower disclosed in Patent Document 1 is described below with reference to FIGS. 8A and 8B.
As shown in FIGS. 8A and 8B, multiblade air blower 101 includes multiblade fan 105 (hereafter referred to as “fan 105”), scroll casing 107, and orifice 110. Fan 105 includes round end plate 102 and a plurality of multiple blades 104. One end of each of blades 104 is fixed to one face periphery 103 of round end plate 102. The other ends of blades 104 are connected at their outer periphery. Scroll casing 107 houses fan 105, and guides air taken in from front inlet 106 of fan 105 in a centrifugal direction. One corner of inner periphery 108 of the other end of each blade 104 is notched so that tips 109 of blades 104 are overlaid on orifice 110. Orifice 110 configures front inlet 106.
In the above structure, blade inner diameter Db 1 and orifice inner diameter Do1 have the same dimensions, and multiblade air blower 101 has blades 104 that are long in the direction of rotational axis.
Next, another conventional multiblade air blower is disclosed (Refer to Patent Document 2.) The conventional multiblade air blower disclosed in Patent Document 2 is described below with reference to FIG. 9. As shown in FIG. 9, multiblade air blower 201 includes multiblade fan 205, fan motor 213, and scroll casing 207. Fan 205 has multiple blades 204. Fan 205 is fixed to motor shaft 212 of fan motor 213. Fan 205 is housed inside of scroll casing 207, and spiral scroll chamber 214 is formed around the outer periphery of fan 205.
In addition, scroll casing 207 includes intake side case plate 216 and motor side case plate 217. Intake side case plate 216 has air inlet 215. Motor side case plate 217 is positioned at the opposite side of intake side case plate 216 with fan 205 in between. A motor body of fan motor 213 is fixed to motor side case plate 217. Backflow suppression device 218 is provided at an outside of fan diameter Df2. Backflow suppression device 218 suppresses backflow of air in scroll chamber 214 to flow back from scroll chamber 214 to air inlet 215 via an intake space between fan 205 and intake side case plate 216.
This structure suppresses the backflow of air to air inlet 215 from scroll chamber 214 via space 220 between blades 204 and orifice 210. In addition, since blade inner diameter Db2 is smaller than orifice diameter Do2, airflow to tips 209 of blades 204 is enhanced.    Patent Document 1: Japanese Patent Unexamined Publication No. H10-185238    Patent Document 2: Japanese Patent Unexamined Publication No. 2002-161890 20